Package structure with a retarding structure and method of making same

ABSTRACT

An encapsulant easily flows into a space between a substrate and an electronic device and contacts with an active region of the electronic device to affect the characteristic of the electronic device in the conventional arts. The present invention provides a package structure with a retarding structure to efficiently avoid the problem. The package structure comprises an electronic device, a substrate, a retarding structure, and an encapsulant. The substrate has conductive contacts disposed on an upper surface. The electronic device has an active region and conductive pads disposed on a first surface. The electronic device is electrically coupled to the substrate by conductive bumps between the conductive contacts and the corresponding conductive pads. The encapsulant is formed around a periphery of the electronic device. The retarding structure is disposed outside the active region on the first surface of the electronic device for avoiding the encapsulant contacting the active region of the electronic device.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.10/701,900, filed Nov. 4, 2003, which is hereby incorporated byreference in its entirety.

TECHNICAL FIELD

This invention relates to a Flip-Chip package structure, and moreparticularly to a package structure with a retarding structure.

BACKGROUND

The Flip-Chip technology is an advanced package technology forconnecting chip and substrate. During packaging process, the chip is“flipped” and so the pads of the chip connect with the pads of thesubstrate. The materials of substrate suitable for Flip-Chip generallyinclude ceramic substrate, silicon wafer, polymer, glass and so on. Theflip-Chip technology thereof is widely applied in RF components,sensors, microprocessor, CCD, semiconductor lasers, LED, SAW (surfaceacoustic wave) device, Multi-chip Modules (MCM), etc., which is used forcomputer, PCMCIA card, martial equipment, personal communications,clocks, watches, LCD, and so on.

Flip-Chip technology has two main advantages. First, the signaltransmitting distance between a chip and a substrate can be reduced andso it is suitable for packaging a high-speed device; second, the size ofthe packaged chip can be reduced as the size of chip before packaging,so it is suitable for the IC device requiring a smaller packaging size.

In those conventional arts, the Flip-Chip package structure ofelectronic devices is accomplished by forming bumps on pads of thesurface of electronic devices (or on the substrate side), and connectingthose bumps to pads on the substrate side (or the surface of electronicdevices). After the Flip-Chip packaging, the gap between each electronicdevice and the substrate is sealed with resin to ease stress, to preventthe invasion of foreign matter, and to protect the bumps. However, ifany foreign matter sticks to the surface of a GaAs element or a surfaceacoustic wave element, which is operable at a high frequency, thedesired electric characteristics cannot be obtained, and therefore thegap between the substrate and the element should have an airtightstructure, with the element covered by a resin all around.

To meet this requirement, a structure, in which the gaps between thesubstrate and the electronic devices are made airtight, is formed bydropping a resin of high viscosity type, which would not enter into thegaps between the substrate and the electronic devices, on the electronicdevices and hardening it.

However, in a structure wherein Flip-Chip package electronic devices arecovered with resin, signals often cannot be transmitted and fail toachieve the desired characteristics, since the resin enters through thegaps between the substrate and the electronic devices to come intocontact with an active region of the electronic devices.

To avoid the aforementioned problem, in the U.S. Pat. No. 5,969,461, itdiscloses a structure of Underfill package technology. Referring to FIG.1A, the resin 140 will flow into the space between the acoustic wavedevice 110 and the substrate 120 during the time from injecting theresin 140 to the resin 140 having been cured. Therefore, the dam 130 isdisposed on the substrate 120 within the periphery 122 of the acousticwave device 110 and interconnections formed by stud bumps 123 andconductive materials 124 for avoiding the resin 140 contacting with theactive region of the acoustic wave device 110 and affecting thecharacteristic of the acoustic wave device. However, because the dam 130is disposed within the stud bumps 123 and the conductive materials 124,the specific position relationships among the dam 130, the stud bumps123, and the conductive materials 124 must be accurate, which increase acomplexity of the process. Furthermore, the dam 130 is close to anactive region of the acoustic wave device 110 and when the dam 130 doesnot abut a face 114 of the acoustic wave device 110, the resin 140easily contacts with the active region as long as the resin 140 lightlyflows over the dam 130.

Referring to FIG. 1B, the U.S. Pat. No. 6,262,513 discloses anotherencapsulation resin package technology. A resin layer 240 covers on anelectronic device 210 and the substrate 220. A fluiding of the resinlayer 240 must be low or no flow for avoiding flowing the resin layer240 into the space between the electronic device 210 and the substrate220 and affecting the characteristic of the electronic device as theUnderfill package technology. Nevertheless, the resin layer 240 has theproblem of thermal expansion when heating to cure the resin. A SiO2 isadded into the resin layer 240 in order to reduce a thermal stress dueto the difference of thermal expansion coefficient, but it results indecreasing the adhesion between the resin layer 240 and wires 290 andthe hermeticity of the structure is so unsatisfactory.

In the U.S. Pat. No. 6,448,635, is also discloses a structure ofUnderfill package technology. As shown in FIG. 1C, a distance D1 betweenactive region 340 and the adjacent peripheral surface 338A or 338C ismore than 550 μm, and a distance D2 between each peripheral side surface338B or 338D and the active region 340 is more than 200 μm. Referring toFIG. 1D, these distances prepare against the flowing of an encapsulant306. Therefore, the encapsulant 306 extends under SAW device 332A, butthe encapsulant 306 does not extend inward from each of surfaces 338Aand 338C more than 550 μm. Therefore, the area of not active region isvery large and, the packaged size will increase.

SUMMARY

In those conventional arts, the Flip-Chip technology has a problem thatthe encapsulant flows into a space between a substrate and an electronicdevice and contacts with an active region of the electronic device toaffect the characteristic of the electronic device. One of objectives ofthe present invention is to provide a package structure for avoiding theencapsulant contacting with the active region.

Another objective of present invention is to provide a simple andlow-cost package structure.

As aforementioned, the present invention provides a package structurewith a retarding structure. The package structure comprises anelectronic device, a substrate, a retarding structure, and anencapsulant. The substrate has conductive contacts disposed on an uppersurface. The electronic device has an active region and conductive padsdisposed on a first surface. The electronic device is electricallycoupled to the substrate by conductive bumps between the conductivecontacts and the corresponding conductive pads. The encapsulant isformed around a periphery of the electronic device. The retardingstructure is disposed outside the active region on the first surface ofthe electronic device for avoiding the encapsulant contacting the activeregion of the electronic device.

The present invention also provides another package structure with aretarding structure. The package structure comprises an electronicdevice, a substrate, a trench, and an encapsulant. The substrate hasconductive contacts disposed on an upper surface. The electronic devicehas an active region and conductive pads disposed on a first surface.The electronic device is electrically connected to the substrate byconductive bumps between the conductive contacts and the correspondingconductive pads. The trench is formed around a periphery of theelectronic device and outside the active region on the first surface ofthe electronic device for avoiding the encapsulant contacting the activeregion of the electronic device.

The present invention also provides a method for packing an electronicdevice. The method comprising the steps of: providing a substrate havingconductive contacts disposed on an upper surface thereof; providing anelectronic device having an active region and conductive pads disposedon a first surface thereof; forming a retarding structure outside theactive region on a first surface of the electronic device; connectingthe electronic device onto the substrate by means of conductive bumpsbetween the conductive contacts and corresponding the conductive pads;flowing an encapsulant at a periphery of the electronic device; andcuring the encapsulant to harden the encapsulant for avoiding theencapsulant contacting with the active region of the electronic device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of a structure of underfill packagetechnology in the conventional arts;

FIG. 1B is a schematic diagram of a structure of encapsulation resinpackage technology in the conventional arts;

FIG. 1C and FIG. 1D are schematic diagrams of another structure ofunderfill package technology in the conventional arts;

FIG. 2A is a schematic diagram of an encapsulant flowing into a spacebetween an electronic device and a substrate due to capillary phenomenonaccording to this invention;

FIG. 2B shows a schematic diagram of one preferred embodiment in thepresent invention;

FIG. 3A shows a schematic diagram of another preferred embodiment in thepresent invention; and

FIG. 3B is a schematic diagram of a trench formed before a cuttingprocess in accordance with this invention.

DETAILED DESCRIPTION

Some sample embodiments of the invention will now be described ingreater detail. Nevertheless, it should be recognized that presentinvention can be practiced in a wide range of other embodiments besidesthose explicitly described, and the scope of the present invention isexpressly not limited expect as specified in the accompanying claims.

Then, the components of the different elements are not shown to scale.Some dimensions of the related components are exaggerated andmeaningless portions are not drawn to provide a more clear descriptionand comprehension of the present invention.

Due to capillary phenomenon, an encapsulant flows into a space betweenan electronic device and a substrate during duration from theencapsulant flowing around the electronic device to the encapsulantbeing cured and a characteristic of the electronic device is changed.According to our observation, the encapsulant 40 mainly flows into thespace along a surface 15 of the electronic device 10, as shown in FIG.2A. Therefore, the essence of the present invention is to increase aretarding structure for resisting the capillarity between the electronicdevice and the encapsulant.

FIG. 2B shows a package structure of one preferred embodiment in thepresent invention. The package structure comprises an electronic device10, a substrate 20, a retarding structure 30, and an encapsulant 40. Thesubstrate 20 has conductive contacts 22 disposed on an upper surface 24.The electronic device has an active region 12 and conductive pads 14disposed on a first surface 16. The electronic device 10 is electricallycoupled to the substrate 20 by conductive bumps 18 between theconductive contacts 22 and the corresponding conductive pads 14. Theencapsulant 40 is formed around a periphery of the electronic device 10.The retarding structure 30 is disposed outside the active region 12 onthe first surface 16 of the electronic device 10 for avoiding theencapsulant 40 contacting the active region 12 of the electronic device10.

The retarding structure 30 can be a protruding structure in theembodiment and a height thereof is preferably in the range of 20-40percent of a distance between the substrate 20 and the electronic device10, e.g. the distance between the substrate 20 and the electronic device10 is 30 μm and the height of the retarding structure 30 isapproximately 10 μm. The retarding structure 30 can be any material,such as a metal or a resin that includes epoxy, silicone, polyimide, andbenzocyclobutene, even be that as same as the encapsulant 40. If theretarding structure 30 is made of a resin, it is preferably to perform acuring process to harden the retarding structure 30 before flowing theencapsulant 40 at a periphery of the electronic device 10.

In order to add the buffer distance between the active region and theretarding structure, the retarding structure is disposed outside of theconductive pads. Therefore, it is surer that the encapsulant is harderto extend to contact with the active region.

The formation method of the retarding structure may be a screen printingmethod or a photolithography method. Especially, the screen printing isa low-cost method with controllable yield.

In general, the encapsulant has a low fluidity at a low temperature, butthe fluidity will gradually increase when the temperature graduallyraises. Hence, the encapsulant mainly flows into the space between theelectronic device and the substrate during a curing process for theencapsulant.

In order to reduce the wetting issue from capillary phenomenon, exceptfor the aforementioned high viscosity, the material of the encapsulantmore preferably has the following characteristics: (1) low or no flowfluiding; (2) solvent-free; and (3) thixotropic fluid. The property ofthixotropy enables fluid to stiffen in a relatively short time onstanding, but upon shear force to change to a very soft consistency orto a fluid of high velocity. The addition of suitable fillers toencapsulant can have the above flow characteristics. Exemplary fillersinclude an unconductive aluminum compound, e.g.: alumina, aluminumnitride, kaolin (Al₂Si₂O₅(OH)₄), and so on. Owing to thixotropy, theencapsulant can be easily dispensed by using conventional needledispenser, such as Musashi dispenser.

Moreover, the retarding structure may be a trench. FIG. 3A shows apackage structure of another preferred embodiment in the presentinvention. The package structure comprises an electronic device 10, asubstrate 20, a trench 50, and an encapsulant 40. The substrate 20 hasconductive contacts 22 disposed on an upper surface 24. The electronicdevice has an active region 12 and conductive pads 14 disposed on afirst surface 16. The electronic device 10 is electrically connected tothe substrate 20 by conductive bumps 18 between the conductive contacts22 and the corresponding conductive pads 14. The trench 30 is formedaround a periphery of the electronic device 10 and outside the activeregion 12 on the first surface 16 of the electronic device 10.

In the conventional arts, it needs to add the distances between theactive region and peripheral side surfaces to prepare against theflowing of the encapsulant. In the present invention, the trench can addthe flowing path of the encapsulant for encapsulant spreading and keepthe distance between the active region and peripheral side surfaces.Furthermore, the trench also increases the roughness of a first surface16. The encapsulant 40 can be avoided contacting the active region 12 ofthe electronic device 10 without adding the die size in the presentinvention.

A depth of the trench 50 is preferably more than 150 μm, and the widthof the trench 50 is more than 150 μm. The trench 50 with theaforementioned depth and width can efficiently avoid the encapsulant 40flowing into the space between the substrate 20 and the electronicdevice 10 and contacting with the active region 12.

In order to add the buffer distance between the active region and thetrench, the trench is formed outside of the conductive pads. Therefore,it is surer that the encapsulant is hard to extend to contact with theactive region. The trench 50 is preferably formed before a cuttingprocess for dividing into each of the electronic devices 10 on a wafer60, as shown in FIG. 3B.

The forming method of the trench 50 may be a half cutting, asand-blasting or etching process. Before the sand-blasting or etchingperforms, a protecting layer, e.g. preform film or photolithographydefined mask, is covered on the electronic device 10 expect for the areacorresponding the trench 50. Next, the sand-blasting or etching processforms trench 50 and then the protecting layer is removed.

The retarding structure also can be formed on the substrate to reducingthe wetting issue. The retarding structure on the substrate also canincrease the roughness and the effective distance for encapsulantspreading.

As aforementioned, in order to reduce the wetting issue from capillaryphenomenon, the material of the encapsulant has the followingcharacteristics: (1) high viscosity; (2) low or no flow fluiding; (3)solvent-free; and (4) thixotropic fluid. The addition of suitablefillers to epoxy can have the above flow characteristics. Exemplaryfillers include an unconductive aluminum compound, e.g.: alumina,aluminum nitride, kaolin (Al₂Si₂O₅(OH)₄), and so on.

According to the above-mentioned, the present invention also discloses amethod for packing electronic device. The method is preformed as below.First, a substrate is provided and conductive contacts are disposed onan upper surface of the substrate. Next, an electronic device isprovided, that has an active region and conductive pads disposed on afirst surface thereof. Then, a retarding structure is formed outside theactive region. Subsequently, the electronic device is flipped onto thesubstrate and the first surface of the electronic device faces the uppersurface of the substrate, and the conductive contacts and thecorresponding conductive pads are connected by means of conductivebumps. An encapsulant is flowed at a periphery of the electronic device,and finally the encapsulant is cured for avoiding the encapsulantcontacting with the active region of the electronic device.

The retarding structure may be a protruding structure or a trench. Whenthe retarding structure is a protruding structure and made of a resin,the method further comprises a step of curing the retarding structure.

Types of the electronic device 10 applied with the present inventionwill not be limited. For example, the package assembly and the method ofthe present invention can apply to RF components, sensors, EPROM, CCD,semiconductor lasers, LED, SAW (surface acoustic wave) device and so on.

Hence, compared with the conventional arts having the aforementioneddrawbacks, the present invention employs a retarding structure betweenthe electronic device and the substrate to overcome the conventionaldrawbacks. The retarding structure not only efficiently avoids theencapsulant contacting with the active region, but also is a simple andlow-cost package structure.

Although specific embodiments have been illustrated and described, itwill be obvious to those skilled in the art that various modificationsmay be made without departing from what is intended to be limited solelyby the appended claims.

1. A method for packing an electronic device, comprising the steps of:providing a substrate having conductive contacts disposed on an uppersurface thereof; providing an electronic device having an active regionand conductive pads disposed on a first surface thereof; forming aretarding structure that is a trench outside said active region on afirst surface of said electronic device; connecting said electronicdevice onto said substrate by means of conductive bumps between saidconductive contacts and corresponding said conductive pads; flowing anencapsulant at a periphery of said electronic device; and curing saidencapsulant to harden said encapsulant for avoiding said encapsulantcontacting with said active region of said electronic device.
 2. Themethod in claim 1, wherein said electronic device is a surface acousticwave device.
 3. The method in claim 1, wherein said encapsulantcomprises an unconductive aluminum compound.
 4. The method in claim 1,wherein a width of said trench is wider than 150 μm.
 5. The method inclaim 1, wherein a depth of said trench is deeper than 150 μm.